You were pretty accurate on describing Katarina's rework. The rework was something that only created more issues with Katarina than actually fixing the ones she had. The problem with old Katarina was that she had pretty much no skill expression. You couldn't tell a good Katarina from a Katarina that just went in and smashed literally every button on her keyboard and got kills. Her laning phase was extremely poor since she lacked sustain, and she had little to no counterplay when she got fed, deleting your whole team in a second.
When Reworking Katarina, Riot tried to fix all these issues, but ended up failing miserably. Before Katarina had no skill expression, now it's to the point where a Katarina main almost feels unfair to play against because she has too much skill expression. Then riot took Katarina's terrible laning phase and gave her one of the strongest level 2-3 all in's in the game. They buffed her base stats, gave her more damage, and gave her an auto reset to top it all off. To fix her counterplay issue, Riot delayed her damage and then made it so you could see exactly where her daggers were, only issue being that she exploits mistakes too hard so if you step too close to the dagger then you're a goner.
There's a few fixes to these issues with Kat -
Nerfing Gunblade - Gunblade itself is an extremely problematic item, providing crazy sustain and acting as basically a fifth ability. The item itself is extremely awful to play against and imo needs to be reworked or removed entirely. Only problem is, if you nerf the item, you're nerfing all of the champions that use it, but most of the champions that use it need to be reworked anyways because of problems they have.
Revert Shunpo - Her auto reset is what makes her laning phase so frustrating, because she is able to do crazy amounts of damage with an Auto E Auto, on top of the fact that shunpo resets, it makes her a nightmare to trade with early on. I think it would be best to remove the auto reset entirely and in return, just revert Katarina's old shunpo. Bring back the old animation and remove the cast time that makes her feel clunky to play, but most importantly, remove her damn auto reset. (When I say revert shunpo I don't mean bring back the wardhop because that'd give WAY too much mobility).
Revert the Entire Rework and Rework her again - While reverting the rework is a long shot, theres no doubt that Katarina has to be reworked again. She exists in a state where she will never be balanced, if she doesn't blow up everyone, shes useless. She's way too frustrating for the enemy team to play against. Riot has to start from scratch and give her a full rework, and not some shitty class update rework, and ACTUALLY fix the problems with her.